U.S. patent number 6,557,534 [Application Number 09/753,388] was granted by the patent office on 2003-05-06 for canister purge strategy for a hybrid electric vehicle.
This patent grant is currently assigned to Ford Global Technologies, Inc.. Invention is credited to Stephen John Kotre, Jerry D. Robichaux.
United States Patent |
6,557,534 |
Robichaux , et al. |
May 6, 2003 |
Canister purge strategy for a hybrid electric vehicle
Abstract
The present invention provides a method and system for purging a
vapor canister in a Hybrid Electric Vehicle during vehicle idle
conditions. The present invention first determines whether purging
is necessary by measuring fuel tank pressure and the time since the
last purge. If either of these elements exceeds a calibratable
threshold, the controller determines that the engine needs to be on
and that purging must occur. An electronic throttle controller can
also be used to command the throttle plate to low positions to
increase intake manifold vacuum while purging. This allows for very
rapid ingestion of the fuel vapor without risk of engine stalls, if
used in an HEV where the engine speed is controlled by an electric
motor. Upon completion of the purging process, the engine is shut
"off" and the vehicle is returned to its normal idle
conditions.
Inventors: |
Robichaux; Jerry D. (Tucson,
AZ), Kotre; Stephen John (Ann Arbor, MI) |
Assignee: |
Ford Global Technologies, Inc.
(Dearborn, MI)
|
Family
ID: |
32108583 |
Appl.
No.: |
09/753,388 |
Filed: |
January 3, 2001 |
Current U.S.
Class: |
123/520;
123/179.16; 903/903 |
Current CPC
Class: |
B60K
6/445 (20130101); F02M 25/08 (20130101); B60W
20/15 (20160101); B60W 10/24 (20130101); F02D
41/0032 (20130101); B60W 20/00 (20130101); F02D
35/0007 (20130101); F02N 11/0829 (20130101); B60W
10/06 (20130101); F02D 11/105 (20130101); B60K
6/00 (20130101); B60W 2710/065 (20130101); Y02T
10/6239 (20130101); Y02T 10/54 (20130101); Y10S
903/903 (20130101); F02D 2200/0406 (20130101); Y02T
10/62 (20130101); B60W 2510/0671 (20130101); Y02T
10/48 (20130101); Y02T 10/40 (20130101); F02D
41/08 (20130101); B60W 2710/0605 (20130101); F02D
2200/0602 (20130101) |
Current International
Class: |
B60K
6/00 (20060101); B60K 6/04 (20060101); F02D
35/00 (20060101); F02D 41/00 (20060101); F02M
25/08 (20060101); F02D 11/10 (20060101); B60K
1/02 (20060101); B60K 1/00 (20060101); F02D
41/08 (20060101); F02M 033/02 () |
Field of
Search: |
;123/518,519,520,179.16 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Moulis; Thomas N.
Attorney, Agent or Firm: Hanze; Carlos L.
Claims
We claim:
1. A method of purging a vapor canister in a hybrid electric
vehicle during vehicle idle conditions comprising the steps of:
determining if vehicle idle conditions are met; determining if a
purging process has been executed for a recent drive cycle;
determining fuel tank pressure; comparing fuel tank pressure to a
calibratable pressure threshold; determining the time since last
purge; comparing time since last purge to a calibratable time
threshold; starting an engine; purging by opening a valve between
the vapor canister and an intake manifold; and controlling a
throttle plate via an electronic throttle controller to increase
vacuum in the intake manifold.
2. A system to purge a vapor canister in a hybrid electric vehicle
during vehicle idle conditions comprising: means for determining if
vehicle idle conditions are met: means for determining if a purging
process has been executed for a recent drive cycle; means for
determining fuel tank pressure; means for comparing fuel tank
pressure to a calibratable pressure threshold; means for
determining time since last purge; means for comparing time since
last purge to a calibratable time threshold; means for starting an
engine; means for opening a valve between the vapor canister and an
intake manifold to start the purge process; and means for
controlling a throttle plate via an electronic throttle controller
to increase vacuum in the intake manifold.
3. The method of claim 1, further comprising: determining a vapor
canister condition.
4. The method of claim 3, wherein determining a vapor canister
condition comprises: determining how far an air/fuel ratio
controller has shifted.
5. The method of claim 3, wherein determining a vapor canister
condition comprises: determining the mass of remaining vapor in the
vapor canister.
6. The method of claim 1, further comprising: stopping the
engine.
7. The method of claim 1, wherein controlling a throttle plate via
an electronic throttle controller to increase vacuum in the intake
manifold comprises: controlling the throttle plate to a
calibratable position.
8. The system according to claim 2, further comprising a purge
control strategy embodied in a vehicle system controller.
9. The system according to claim 2, further comprising a purge
control strategy embodied in an engine control unit.
10. The system according to claim 2, wherein the means for
determining fuel tank pressure comprises a fuel tank pressure
transducer electronically connected to an engine control unit.
11. The system according to claim 2, wherein the means for opening
a valve between the vapor canister and an intake manifold to start
the purge process comprises an electric vapor management valve
electronically connected to an engine control unit.
12. The system according to claim 2, further comprising: means for
determining a vapor canister condition.
13. The system according to claim 12, wherein the means for
determining a vapor canister condition comprises: means for
determining how far an air/fuel ratio controller has shifted.
14. The system according to claim 12, wherein the means for
determining a vapor canister condition comprises: means for
determining the mass of remaining vapor in the vapor canister.
15. The system according to claim 2, further comprising; means for
stopping the engine.
16. The system according to claim 2, wherein the means for
controlling a throttle plate via an electronic throttle controller
to increase vacuum in the intake manifold comprises: means for
controlling the throttle plate to a calibratable position.
17. A system for purging a vapor canister in a hybrid electric
vehicle that includes an engine and a starter for said engine,
comprising: an electronic throttle controller and a throttle plate
in an intake manifold of said engine; a controller connected by
means of a network to said electronic throttle controller; a
strategy in said controller for determining if a purging process
has been executed for a recent drive cycle including a clock for
determining whether a preselected minimum time since last purge has
elapsed; a pressure transducer operatively connected to the
controller for determining fuel tank pressure; a controller
strategy for comparing fuel tank pressure against a preselected
pressure threshold; a valve controlled by said controller between
the vapor canister and an intake manifold to start the purge
process; and a controller strategy for causing said electronic
throttle controller to control said throttle plate to increase
vacuum in said intake manifold of said engine.
18. The system according to claim 17, further comprising a
controller strategy to determine a vapor canister condition.
19. The system according to claim 18, wherein the controller
strategy to determine a vapor canister condition comprises a
controller strategy to determine how far an air/fuel ratio
controller has shifted.
20. The system according to claim 18, wherein the controller
strategy to determine a vapor canister condition comprises a
controller strategy to determine the mass of remaining vapor in the
vapor canister.
21. The system according to claim 17, wherein the controller
strategy for causing said electronic throttle controller to control
said throttle plate to increase vacuum in said intake manifold of
said engine controls said electronic throttle plate to a
calibratable position.
Description
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a Hybrid Electric Vehicle ("HEV")
where a vehicle system controller or engine controller determines
if a canister collecting fuel vapor needs to be purged during
vehicle idle.
2. Discussion of the Prior Art
The need to reduce fossil fuel consumption and pollutants of
automobiles and other vehicles powered by Internal Combustion
Engines ("ICEs") is well known. Vehicles powered by electric motors
have attempted to address these needs. However, electric vehicles
have limited range and limited power coupled with the substantial
time needed to recharge their batteries. An alternative solution is
to combine both an ICE and electric traction motor into one
vehicle. Such vehicles are typically called Hybrid Electric
Vehicles ("HEVs"). See generally, U.S. Pat. No. 5,343,970
(Severinsky).
The HEV has been described in a variety of configurations. Many HEV
patents disclose systems where an operator is required to select
between electric and internal combustion operation. In others, the
electric motor drives one set of wheels and the ICE drives a
different set.
Other configurations have developed. A Series Hybrid Electric
Vehicle ("SHEV") is a vehicle with an engine (most typically an
ICE) which powers a generator. The generator, in turn, provides
electricity for a battery and motor coupled to the drive wheels of
the vehicle. There is no mechanical connection between the engine
and the drive wheels. A Parallel Hybrid Electrical Vehicle ("PHEV")
is a vehicle with an engine (most typically an ICE), battery, and
electric motor combined to provide torque to power the wheels of
the vehicle.
A Parallel/Series Hybrid Electric Vehicle ("PSHEV") has
characteristics of both a PHEV and a SHEV. The PSHEV is also known
as a torque (or power) splitting powertrain configuration. Here,
the torque output of the engine is given in part to the drive
wheels and in part to an electrical generator. The electric
generator powers a battery and motor that also provide torque
output. In this configuration, torque output can come from either
source or both simultaneously. In this configuration the vehicle
braking system can even deliver torque to drive the generator to
produce charge to the battery.
The desirability of combining an ICE with an electric motor is
clear. The combination provides the opportunity to reduce the ICE's
fuel consumption and pollutants with no appreciable loss of
performance or range of the vehicle. Nevertheless, there remains
substantial room for development of ways to optimize these HEV's
operational parameters.
One such area of improvement is the HEV's tailpipe and evaporative
emission control systems. Tailpipe emissions require very tight
control of the Air to Fuel ratio (A/F). Controlling the A/F ratio
requires an oxygen sensor to measure the amount of oxygen leaving
the engine after combustion. A controller then monitors the oxygen
levels and controls the amount of fuel provided by the injectors in
an attempt to create an optimal A/F ratio, thereby reducing
unwanted emissions.
Controlling the A/F ratio becomes more complex when fuel vapor is
considered. Fuel vapor is generated in the fuel system (tank and
lines) because of the heat of the fuel when the engine is running
at its stabilized operating temperature. If not managed properly,
the vapor can build, causing the fuel vapor pressure to increase to
the point where the vapor can leak out of the fuel system into the
atmosphere as unwanted evaporative emissions. Thus, a charcoal
canister is typically installed between the fuel tank and the
engine to collect the fuel vapor. Over time, the canister becomes
full and must be emptied or purged. In order to purge, a vapor
management valve (VMV) is opened in a controlled manner by a VMV
controller, thereby allowing the fuel vapor into the intake
manifold, as long as there is sufficient vacuum present inside the
manifold. During the purging process, the A/F controller maintains
the optimum A/F ratio (and thus compensates for the additional fuel
vapor entering the cylinders) by adjusting the fuel amount
delivered by the injectors. Then, the VMV controller determines
when the canister is empty and closes the VMV. Specifically, the
VMV controller determines the canister's condition by estimating
how much fuel vapor is being drawn into the intake manifold and
cylinders. The amount that the A/F controller must correct the fuel
delivery through the fuel injectors when the purging process is
occurring reflects how much fuel vapor is coming from the vapor
canister and causing the A/F disturbance.
Although it is desirable to purge the canister as quickly as
possible, the rate of purging must be controlled. If the purge
valve opens too quickly, especially if the intake manifold is in a
high vacuum condition, the A/F controller may not be able to
compensate fast enough for the incoming fuel vapor. This, in turn,
can cause the A/F ratio to become too lean and causes poor engine
combustion. In a conventional vehicle, if the A/F is too lean, the
engine could stall. Thus, in conventional vehicles (and perhaps
some HEV configurations), even though the vapor canister can be
purged faster if the VMV is opened quickly and if higher vacuum
conditions are present in the intake manifold, the risk exists that
the engine may stall.
HEVs present additional purge problems. First, the engine is not
always running, particularly during idle conditions (when the
vehicle is not in motion). The canister can still store vapor, but
it is not possible to purge the canister if the engine is not
running.
Second, some HEVs run the engine at near wide-open throttle
conditions (when the engine is running) because it is more
fuel-efficient. However, little or no vacuum is available to draw
the vapor into the intake manifold when the VMV is opened. This, in
turn, makes it very difficult to purge the vapor canister.
Finally, most engine control systems implement an adaptive fuel
strategy that "learns" or "adapts" the long term fuel shifts in the
fuel delivery system caused by variation in fuel system components
(injectors and mass air flow sensor). A typical engine control
system does not allow the purging process to occur while the
adaptive fuel shifts are learned because the purging process
introduces A/F ratio shifts that should not be attributed to the
fuel delivery system but rather to purge vapor. Thus, for the
reduced amount of time that the engine is running during an HEV
drive cycle, the adaptive fuel and purge strategies are competing
for time to accomplish their objective.
The aforementioned issues make it difficult to purge the vapor
canister often enough during a given HEV drive cycle. This
increases the risk that fuel vapors will be released into the
environment, which is not consistent with current emission goals
and standards. Therefore, it is desirable to develop a method of
purging the canister of an HEV to minimize the release of fuel
vapor to the environment.
SUMMARY OF THE INVENTION
The present invention provides a method and system for purging a
vapor canister in an HEV. Even though this invention is for an HEV,
it uses a conventional-type purge control strategy that runs
normally when the engine is "on" and conventional purging
conditions are met (such as the adaptive fuel strategy is not
running). This strategy includes the vehicle idle modes encountered
in an HEV drive cycle where the engine is required to be "on" for
reasons other than purging the vapor canister. The reasons include
but are not limited to battery charging and running the air
conditioner if mechanically driven by the engine front end
accessory drive belt, etc.
When the engine is running, it is not always at an optimal point
for purging (low vacuum or adaptive fuel strategy is running).
Further, since most vehicle idle modes have the engine "off", the
vapor canister status and purge must be monitored at appropriate
times to insure efficiency and emissions goals are met. The best
opportunity for doing this is when the vehicle is at idle.
The present invention forces the engine to remain (or turn) on at
vehicle idle conditions to purge the vapor canister if required by
certain canister conditions. These canister conditions can include,
but are not limited to, fuel tank pressure and the time lapse since
the last purge cycle exceeding a calibratable threshold. Once it is
determined that purging is required, the engine is turned on (if
not already on) and is commanded to operate at lower throttle
positions so that more vacuum is available in the intake manifold
to draw in the fuel vapor. This part of the invention can only be
accomplished if an electronic throttle controller is used with the
engine.
In some HEV configurations where the engine speed is controlled by
an electric motor (such as a PSHEV or "powersplit"), these very
high intake manifold vacuum conditions can be forced via throttle
control without risking an engine stall. If the A/F ratio were too
lean because the A/F controller cannot accommodate the incoming
fuel vapor, the engine would not stall because of poor combustion.
The electric motor controls the engine speed. The controller then
maintains the engine running in this high vacuum state until the
vapor canister is empty so that the purging process can be stopped
and the engine turned "off" again during vehicle idle
conditions.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates the configuration of a basic powersplit Hybrid
Electrical Vehicle.
FIG. 2 illustrates the general layout of a fuel system and an
exhaust system.
FIG. 3 is a flow chart illustrating the HEV purging process.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention relates to Electric Vehicles and, more
particularly, Hybrid Electric Vehicles (HEVs). FIG. 1 demonstrates
just one possible configuration, specifically a Parallel/Series
Hybrid Electric Vehicle (powersplit) configuration.
In a basic powersplit HEV, a Planetary Gear Set 20 mechanically
couples a Carrier Gear 22 to an Engine 24 via a One Way Clutch 26.
The Planetary Gear Set 20 also mechanically couples a Sun Gear 28
to a Generator Motor 30 and a Ring (output) Gear 32. The Generator
Motor 30 also mechanically links to a Generator Brake 34 and is
electrically linked to a Battery 36. A Traction Motor 38 is
mechanically coupled to the Ring Gear 32 of the Planetary Gear Set
20 via a Second Gear Set 40 and is electrically linked to the
Battery 36. The Ring Gear 32 of the Planetary Gear Set 20 and the
Traction Motor 38 are mechanically coupled to Drive Wheels 42 via
an Output Shaft 44.
The Planetary Gear Set 20, splits the Engine 24 output energy into
a series path from the Engine 24 to the Generator Motor 30 and a
parallel path from the Engine 24 to the Drive Wheels 42. Engine 24
speed can be controlled by varying the split to the series path
while maintaining the mechanical connection through the parallel
path. The Traction Motor 38 augments the Engine 24 power to the
Drive Wheels 42 on the parallel path through the Second Gear Set
40. The Traction Motor 38 also provides the opportunity to use
energy directly from the series path, essentially running off power
created by the Generator Motor 30. This reduces losses associated
with converting energy into and out of chemical energy in the
Battery 36 and allowing all Engine 24 energy, minus conversion
losses, to reach the Drive Wheels 42.
A Vehicle System Controller (VSC) 46 controls many components in
this HEV configuration by connecting to each component's
controller. The Engine Control Unit (ECU) 48 connects to the Engine
24 via a hardwire interface. The ECU 48 and VSC 46 can be based in
the same unit, but are actually separate controllers. The HEV purge
control, which is the subject of this invention, can be handled in
either the VSC 46 or ECU 48. The VSC 46 communicates with the ECU
48, as well as a Battery Control Unit (BCU) 50 and a Transaxle
Management Unit (TMU) 52 through a communication network, such as a
Controller Area Network (CAN) 54. The BCU 50 connects to the
Battery 36 via a hardwire interface. The TMU 52 controls the
Generator Motor 30 and Traction Motor 38 via a hardwire
interface.
FIG. 2 illustrates the general layout of a typical fuel system,
exhaust system, for the Engine 24. A Fuel Tank 70 supplies the fuel
to Fuel Injectors 92 via a Conventional Fuel Pump 74. A
conventional Vacuum Relief Valve 72 is provided on the Fuel Tank 70
cap for equalizing pressure applied to the Fuel Tank 70. The Fuel
Tank 70 further includes a Fuel Tank Pressure Transducer 78 that
senses fuel tank vapor pressure and sends the signal to the ECU
48.
A fuel Vapor Canister 80 is provided for trapping, storing, and
subsequently releasing fuel vapor dispelled from the Fuel Tank 70
for combustion into the Engine 24. An Electric Vapor Management
Valve ("EVMV") 84, when closed, prevents fuel vapor from escaping
into the Engine 24 and diverts it to the Vapor Canister 80. When
opened, the EVMV 84 allows fuel vapor to flow into the Intake
Manifold 86 of Engine 24. The Vapor Canister 80 is connected to the
atmosphere through a Canister Vent Valve 104. A Filter 106 may be
provided between the Canister Vent Valve 104 and the atmosphere for
filtering the air pulled into the vapor Canister 80. The Canister
Vent Valve 104 is a normally open solenoid valve controlled by the
ECU 48.
After combustion, exhaust enters an Exhaust Manifold 90 where an
Oxygen Sensor 100 measures the oxygen level in the exhaust to
determine the A/F ratio. The exhaust then proceeds to a Catalytic
Converter 102 and finally to the atmosphere.
In an HEV, the purging process can only be invoked when the Engine
24 is running. However, when the Engine 24 is running, the
conditions may not allow purging. The HEV Engine 24 typically runs
at or near wide-open throttle to maximize fuel efficiency. This is
not suitable for purging. In addition, an adaptive fuel routine
typically needs to compete with the purging routine for Engine 24
running time to accomplish its tasks.
During the modes when the HEV Engine 24 is not running (the Engine
24 is frequently shut down for fuel efficiency purposes), the
purging process also can not be undertaken even though fuel vapor
can still collect in the Vapor Canister 80. Therefore, it is
necessary to determine when the Engine 24 should be forced "on"
when it would otherwise normally be "off" (particularly at vehicle
idle conditions) so that the purging process can be executed.
The present invention provides a method for purging the Vapor
Canister 80 of an HEV, in particular by commanding the Engine 24 to
come (or stay) "on" during vehicle idle conditions so that the
purging process can be executed, and by controlling the Engine 24
throttle plate (not shown) while purging to provide a high Intake
Manifold 86 vacuum, thereby drawing the fuel vapor in very
rapidly.
To determine whether this HEV purge routine at idle is necessary,
the controller (either VSC 46 or ECU 48) runs through a strategy
that is illustrated in FIG. 3. (It should be noted this invention
is a component part to the patent application for Engine Idle
Arbitration, Invention Disclosure #200-0318.
At Step 200 the vehicle being "keyed on" to start a given HEV drive
cycle. At this step, the controller initializes two parameters used
in the HEV purge routine. The first is PURGE.sub.-- 1 1ST_PASS,
which is initialized to 0, and is used to force the Engine 24 "on"
at the first vehicle idle condition encountered and is used to make
sure the Vapor Canister 80 has a chance to be cleaned for the given
drive cycle, even if the cycle is short in duration. The second
parameter is LAST_PRG_TMR, which is initialized to 0, and is then
allowed to begin counting. This is used to indicate how long it has
been since the purging process was last completed.
The strategy proceeds next to Step 202 where the controller (either
VSC 46 or EMU 48) determines if vehicle idle conditions are met.
These conditions can include, but are not limited to,
determinations of whether the accelerator position (PEDAL_POSITION)
is less than a calibratable threshold and if the vehicle speed
(VEHICLE_SPEED) is less than a calibratable threshold. If these
conditions are not met, the vehicle will remain in its current
driving mode, regardless of whether the Engine 24 is currently "on"
or "off". If the idle conditions are satisfied, then the logic
proceeds to Step 206 and begins an HEV purge routine 206. The first
step in the HEV purge routine 206 is to proceed to Step 208, which
checks to see if PURGE.sub.-- 1 1ST_PASS=0. If PURGE.sub.-- 1
1ST_PASS=0, the purging process is attempted at least once for the
given drive cycle. If yes, the routine proceeds directly to Step
214 where the Engine 24 is started via the command ENGINE--MODE=1
and then to Step 216 where the conventional purge strategy is
invoked via the command PURGE_ENABLE=1. The conventional purge
strategy works by opening the EVMV 84 between the Vapor Canister 80
and the Intake Manifold 86, thereby allowing fuel vapor to enter
the Engine 24 to be combusted.
If PURGE.sub.-- 1ST_PASS=1, then the strategy proceeds to Step 210
where a check is made to see if TANK_PRESSURE exceeds a
calibratable threshold. If yes, the logic goes to Step 214 to start
the Engine 24 and Step 216 to enable the conventional purge
strategy, as described previously.
If TANK_PRESSURE does not exceed the calibratable threshold, the
logic moves to Step 212 where LAST_PRG_TMR is compared to a
calibratable threshold. If LAST_PRG_TMR exceeds the threshold, then
the strategy proceeds directly to Step 214 to start the Engine 24
and Step 216 to enable the conventional purge strategy, as
described previously.
If LAST_PRG_TMR does not exceed the calibratable threshold, then
the strategy jumps directly to a last step, Step 226, where the HEV
purge routine ends and the Engine 24 is allowed to shut off for the
given vehicle idle condition (via ENGINE_MODE=0).
Once the Engine 24 has started at Step 214 and the conventional
purge strategy has invoked at Step 216, the logic proceeds to Step
218 where the Engine 24 throttle plate is commanded to a
calibratable position intended to produce high vacuum conditions in
the Intake Manifold 86. Higher vacuum allows for faster purging
because the fuel vapors will enter the manifold quickly.
Once the purging process has started from Steps 216 and 218, the
logic determines at Step 220 the condition of the Vapor Canister
80. The condition is determined by using conventional methods, such
as using feedback from the oxygen sensor, to determine how far the
A/F controller has shifted due to the introduction of the Fuel Tank
70 vapors into the Intake Manifold 86. This can then be used to
infer the weight or mass of fuel vapor remaining in the Vapor
Canister 80. When this determination is accomplished, Step 222
determines whether the Vapor Canister 80 is sufficiently empty of
fuel vapors. If yes, the logic proceeds to Step 226 where the HEV
purge routine ends and the Engine 24 is allowed to shut off for the
given vehicle idle condition (via ENGINE_MODE=0). If the Vapor
Canister 80 is not considered to be empty, then the strategy
continues the purging process (Step 224) and repeats the Vapor
Canister 80 empty check at Steps 220 and 222 until the Vapor
Canister 80 is clean.
At Step 226, where the HEV purge routine ends and the Engine 24 is
allowed to shut off for the given vehicle idle condition (via
ENGINE_MODE=0), the LAST_PRG_TMR is reset to 0 and then incremented
once again until the next purging sequence occurs.
* * * * *